In general, a cellular telephone includes, as shown in FIGS. 18 and 19, a transmission section A and a reception section B. The transmission section A and the reception section B are turnably connected to each other through a hinge device (not shown). The turning range of the transmission section A and the reception section B is restricted between a folding position as shown in FIG. 18 where the transmission section A and the reception section B are abutted with each other and a using position as shown in FIG. 19, when an angle formed between the transmission section A and the reception section B is, for example 170 degrees.
A hinge device used in the above-mentioned cellular telephone includes, as described, for example, in Japanese Patent Application Laid-Open Nos. 2001-193727 and 2002-106544, a first and a second hinge member which are arranged opposite to each other. The first hinge member is fixed to either the transmission section A or the reception section B of the cellular telephone, and the second hinge member is fixed to the other. The first and second hinge members are turnably connected to each other through a hinge pin. As a result, the transmission section A and the reception section B of the cellular telephone are turnably connected to each other through the hinge device.
The hinge device includes a movable member C and a fixing member D shown in FIG. 20. The movable member C connected to the first hinge member such that the movable member C is non-tunable but movable in the axial direction of the hinge pin. The movable member C is abutted with the fixing member D by a coiled spring (not shown).
A pair of projections C1, C2 are formed on an abutment surface of the movable member C with respect to the fixing member D, and a pair of recesses D1, D2 are formed on an abutment surface of the fixing member D with respect to the movable member C. The pair of projections C1, C2 are arranged such that when the reception section B is located in a position within a predetermined range of angle (biasing angle range) between a folding position and a position away by an angle α toward a using position side from the folding position, the pair of projections C1, C2 are inserted in one end parts of the recesses D1, D2, respectively, in the peripheral direction of the fixing member D. When the projections C1, C2 are inserted in the one end parts of the recesses D1, D2, respectively, the projections C1, C2 are abutted with the slanted bottom surfaces (cam surfaces) of the recesses D1, D2, respectively. By this, the biasing force of the coiled spring is converted into a turn biasing force in one direction (the direction as indicated by an arrow of FIG. 18). By this turn biasing force in one direction, the movable member C is turn biased with respect to the fixing member D and the reception section B is turned to the folding position. Then, the reception section B is maintained in the folding position. When the reception section B is located in the predetermined range of angle (biasing angle range) between a position away by an angle β from the folding position and the using position, the pair of projections C1, C2 are inserted in the other end parts of the recesses D2, D1, respectively, in the peripheral direction of the fixing member D and abutted with the bottom surfaces of the other end parts of the recesses D2, D1, respectively. The bottom surfaces of the other end parts of the recesses D1, D2 are inclined in the direction opposite to the bottom surfaces of one end parts of the recesses D1, D2. Accordingly, when the projections C1, C2 are abutted with the bottom surfaces of the other end parts of the recesses D2, D1, respectively, the biasing force of the coiled spring is converted to a turn biasing force in the other direction (direction as indicated by an arrow of FIG. 19). By this turn biasing force in the other direction, the reception section B is turned to the using position and held in the using position.
If the angle formed between the movable member C and the fixing member D is represented by θ, in the range of angle of α<θ<β, i.e., in the outside of the biasing angle range, the projections C1, C2 are pressed against the fixing member D under the biasing force of the coiled spring, and a frictional resistance is generated therebetween. By this frictional resistance, the movable member C and the fixing member D are stopped at arbitrary positions, and the transmission section A and the reception section B are stopped at arbitrary positions.
The frictional resistance generated between the projections C1, C2 and the fixing member D is comparatively small corresponding to the small biasing force of the coiled spring. For this reason, there is such a problem that it is difficult to keep the transmission section A and the reception section B in the stopping positions stably. To cope with this problem, there can be contemplated that the fraction resistance which is to be generated between the projections C1, C2 and the fixing member D is increased by strengthening the biasing force of the coiled spring. However, the coiled spring is about 3 to 5 mm in diameter and about 0.5 mm in wire diameter. Therefore, there is a certain limit in increasing the biasing force of the coiled spring. If the biasing force of the coiled spring could successfully be increased, the turn biasing force of the coiled spring against the movable member C would overly increased in the biasing angle range. It gives rise to a problem that when the reception section B is turned to the folding position, the reception section B is overly strongly abutted with the transmission section A.